The Virginia Department of Transportation (VDOT) is now taking slugs—otherwise known as “casual carpoolers”—into account when designing commuter parking lots. Although Virginia law prohibits people from soliciting rides on the side of the road, when it comes to slugging, VDOT has recognized the congestion benefits and does not interfere.

As mounting traffic congestion increases the amount of time saved by using HOV lanes, slugging – which combines aspects of traditional carpooling, public transit, and hitchhiking – has been growing in popularity and spreading across the country. According to the website devoted to slugging—Slug-lines.com, slugging developed in the Washington, DC area around 1975, in response to a rules change for the HOV lane on the Shirley Highway (I-95/I-395). The lane, which was opened in 1969, was originally restricted to buses, but in 1975 cars and vans with at least 4 people were permitted to use the lane (the restriction was later relaxed to allow vehicles with 3 occupants as well). Drivers, seeking to avoid the congestion in the general lanes would sometimes pull up next to commuters waiting for the bus and offer rides to commuters headed downtown. Over time, certain bus stops became associated with specific carpooling routes, or slug lines.

The unflattering name for these riders, “slugs,” was originally coined by bus drivers who, seeing them, would pull up to stops expecting them to board the bus but were waved away and began associating these “counterfeit” bus riders with the counterfeit coins, or slugs, that were sometimes used for bus fare by unscrupulous riders. Slugging is now widespread in San Francisco and Houston as drivers have sought congestion relief in HOV lanes by picking up extra passengers, and transportation officials are interested in bring the practice to their cities.

While hitchhiking has been in a long-term decline, and carpooling is at less than half its 1980 level, the decreasing number of young people driving indicates that a turnaround may be on the way. Along with slugging, ridesharing apps, which make it more convenient for people to identify potential drivers and passengers with compatible routes, are gaining popularity and reducing the need for everyone to have a car of their own.